Evaluation of Rock Mass Quality of Phosphorite Mines by Topology Based on Optimal Combination Weight
In order to solve the problem of fuzzy uncertainty of index parameters between adjacent grades of rock quality evaluation,the theory of topology was introduced and the topological rock mass quality grading model based on optimal combination weight was proposed to evaluate the quality of rocks in underground mining of the phosphate mine in Kunyang No.2 mine.According to the geological characteristics of the mine,six influence indexes,namely,uniaxial saturated compressive strength of rock(Rc),rock quality index(RQD),joint spacing(Jd),structural surface condition(Jf),groundwater status(W)and geostress influence coefficient(Z)were selected,and each index was divided into five grades.Then,the subjective and objective weights of the indicators were determined by the improved hierarchical analysis and entropy weight methods,respectively,and the moment estimation method was introduced to optimize the combination of subjective and objective weights.Finally,the modified RMR method and Q-system method were applied to evaluate the quality of the rock mass,and the grading results were compared with the quality classification results of the rock mass based on the optimal combination weights.The results show that,among the five rock masses to be evaluated,the evaluation result for the upper ore body rock is Class Ⅱ,with a characteristic value of 2.57,indicating good rock mass quality and certain self-stabilizing ability.It is determined that the support method of anchor spraying and hanging net should be adopted.For the lower ore body,the characteristic value is 3.68,indicating that the rock mass quality is approaching Class Ⅳ,and the stability of the surrounding rock in the roadway is poor.Immediate initial spraying should be carried out after the excavation of the roadway to control the deformation of the surrounding rock,followed by the use of the anchor spraying and hanging net support method.There are differences in the grading results of the upper ore body N3,and the grading results of the rest of the rock bodies by the proposed method are the same as those of the modified RMR method.The overall low evaluation results using the Q-system method are caused by the failure to take into account the role of geostress and the discontinuity in the grading between the grades.In addition,the model is able to determine the degree to which the rock mass quality grade leans towards the adjacent grade.The classification results are consistent with the geological exploration report of the Kunyang No.2 mine,and are more accurate than the modified RMR method and Q-system method,validating the reliability of the method proposed in this paper and providing technical support for underground mining.
rock mass quality evaluationtopologymaterial element modelmoment estimation methodRMR methodimproved analytic hierarchy process
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